1. Field of the Invention
The present invention relates to a photoelectric converting device and an image processing apparatus utilizing the same.
2. Related Background Art
Among such photoelectric converting devices, there are well known those of a PIN structure utilizing a non-monocrystalline semiconductor. In particular, amorphous semiconductors, represented by amorphous silicon, are widely utilized in one-dimensional line sensors and laminate-structure solid-state image pickup devices, as they can be prepared at a low temperature and in a large area.
However, in such photoelectric converting devices of PIN structure, the P- or N-layer between the pixel electrodes is electrically insulated in order to prevent the leak of signal charge between the pixels, namely crosstalk. This will be explained in more detail with reference to FIGS. 1 and 2.
FIG. 1 is a schematic cross-sectional view of a photoelectric converting device, including a substrate 1301, pixel electrodes 1302, a photoconductive film 1303 composed for example of amorphous silicon, and a transparent electrode 1304.
Such device can be prepared, as disclosed for example in the Japanese Patent Laid-Open Patent No. 58-40985, by forming the pixel electrodes 1302 on the substrate 1301, then forming a photoconductive film 1303, photolithographically eliminating said photoconductive film on the pixel isolation areas, and forming the transparent electrodes 1304.
FIG. 2 is a schematic cross-sectional view of another photoelectric converting device, including a substrate 2401, pixel electrodes 2402, high-density impurity layer 2403, a pixel isolation area 2403', a photoconductive film 2404 for example of amorphous silicon, and a transparent electrode 2405.
The device shown in FIG. 2 can be prepared by forming the pixel electrodes 2402 on the substrate 2401, then forming the high-concentration impurity layer (N- or P-layer) 2403, implanting oxygen or nitrogen ions only in the pixel isolation area 2403' by a photolithographic process, thereby electrically insulating the pixel electrodes, and thereafter forming the photoconductive film 2404 and the transparent electrode 2405. This method is disclosed for example in the Japanese Patent Laid-Open Application No. 60-47574. There is also known a method of eliminating only the pixel isolation area 2403' by etching, as disclosed in the Japanese Patent Laid-Open Patent No. 61-49569.
However, the above-mentioned methods are often associated with various drawbacks. For example, in the example shown in FIG. 1, the etching of the photoconductive film on the pixel isolation area may form a defect in the cross section of the device, thereby causing deterioration of the characteristics, particularly an increase in the dark current. Also the step in the photoelectric converting film frequently results in defects in the transparent electrode, such as breakage.
Also in the example shown in FIG. 2, after the formation of N- or P-layer, the formation of the pixel isolation area by ion implantation or etching requires a photolithographic process, which inevitably deteriorates the surface of said N- or P-layer to generate defects in the N/I or P/I interface, thereby causing deterioration of the device characteristics. Thus, in the above-explained structures, the prevention of deterioration of characteristics of PIN device cannot be often made compatible with the isolation of devices.